The present patent application relates to a pressure container of the type having an outer container enclosing a deformable inner container formed of a metal foil. The inner container forms a chamber for a fill material. The outer container forms a chamber for a propellant. The outer container has a closure part for dispensing the fuel or fill material. Such containers are used in fuel-operated setting tools, wherein they contain the fuel.
Liquid hydrocarbons used as the fuel in the setting tools are stored in pressure vessels. The interchangeable pressure containers or fuel canisters are formed with a dispensing or dosing head attached to the fuel canister by means of a snap-on connection. The pressure container/fuel canister and dispensing head are introduced onto the setting tool. The purpose of the system is to continuously maintain the fuel in the liquid phase for dispensing through the dispensing head. Similar arrangements are made also in other applications of the pressure container, since the release of fuel in the liquid phase is always desirable in the case of devices with liquid fuel dispensing.
There are two conventional systems in the case of pressure containers:                A plastic bag system, in which the liquid fuel is stored in a bag in the container. The bag is comprised of a flexible plastic-aluminum bonded foil and is compressed by the pressure of a gas contained in the outer container such that the inner contents are constantly in a compressed state and remains in the liquid phase. The connection of the bag with the discharge valve is made by a plastic connector, at which diffusion can occur resulting in a mixing of the inner and the outer propellant gas, whereby a failure of the canister can result.        A metal bag system, in which an inner, thin-walled metal container, in particular made of aluminum, is disposed in an outer, thick-walled container (also made of aluminum). At the opening of the pressure container the two containers are rolled up on another, whereby the opening is sealed with a cover piece, in which a valve is arranged, Such a pressure container, for example as disclosed in U.S. Pat. No. 5,069,690, is the basis of the present invention.        
Despite the inherent advantageous tightness of this metal bag system pressure container at the connecting seam of the outer container and the inner container according to U.S. Pat. No. 5,069,590, tightness problems can, however, develop as the result of temperature variations. The metallic inner container is filled with liquid phase fuel in a ready-to-use state of the pressure container, while in the outer container the outer gas is present in part in a liquid phase and in part in a gas phase. When in storage, the pressure container is generally subjected to temperature variations. The liquid phase of the inner container expands at higher temperatures and contracts at lower temperatures. The temperature variations thus result in corresponding variations of the bag volume such that the inner container expands with the expansion of the liquid fuel and again deforms inwardly with contraction of the liquid fuel. Because of these undesirable deformation conditions, local creasing or crumpling spots occur on the metallic inner bag, such spots becoming more and more rigid or imbedded due to cold forming. Consequently, this behavior results in the formation of a hole at the crumpled or crease spot of the inner bag and the pressure container or the canister fails due to leakage.